Discrete superconducting vortex flow transistors

Abstract

In this thesis, two versions of a Discrete Superconducting Vortex Flow Transistor (DVFT) are studied. Both overdamped and underdamped versions are fabricated with low Tc Niobium Josephson junctions. We present analytical models for the operation of the DVFTs that agree with the experimental data. In addition to the operational model of the DVFT, we also present an example of a circuit implementation of the DVFT.Measurements on the overdamped version of the DVFT indicate a current gain of 1.2 when the gate current is injected parallel to the array of junctions. With this manner of gate current injection, the gain is linear in the number of junctions and can be made much greater than 1. Measurements on the underdamped version of the DVFT indicate a transresistance of 2.8Qf with parallel gate current injection.The overdamped DVFT is better suited for circuit implementation than the underdamped version because its operation is nonlatching and is therefore less sensitive to noise.The conclusion of this thesis is that the DVFT is a viable superconducting transistor. The DVFT can be used as a building block to construct complex logic circuitry or as an interface between current based electronics, such as RSFQ logic and voltage based circuits, such as CMOS memory devices.Thesis Supervisor: Terry P. Orlando Title: Professor of Electrical Engineering

Resonance splitting in discrete planar arrays of Josephson junctions

“…As in a single discrete array, the frequencies can be tuned with a control current and are stable for a relatively wide range of bias currents. 1,25 Although the bandwidth is approximately the same as for the single array, a larger output resistance may increase the linewidth. However, phase locking between the two rows is expected to reduce the linewidth, and such measurements will be helpful.…”

“…5͑a͒ and 5͑b͒ show the phase evolution in time for a single set of vertically adjacent junctions near the middle of the array ( jϭ25). The junction phases, 25 (t) and 25 (t), can be approximated by the sum of a linear function in time and a small periodic oscillation. In the V Ϫ state ͑Fig.…”

High current gain HTS Josephson vortex flow transistors

“…JVFTs have a wide range of potential applications such as interfacing superconducting to semiconducting circuits. JVFTs can be based on single long Josephson junctions or an array of discrete short Josephson junctions [6]. The present work is based on the asymmetric N-junction array developed by Gross and co-workers [7-91, with the control line inductively coupled to an array of N-I loops (with dimensions lxw) as shown in Fig.…”

Mapping of one-dimensional Josephson junction arrays onto cellular neural networks

“…(4) the existence of special equilibrium solutions known as vortices are possible which have recently found some applications [2]. We set il = .…”

“…In recent years JJA's have had several applications in the superconducting electronics, e.g. as 1D shift register, transmission line [l] and a superconducting transistor [2]. But in practical applications such arrays have a very complex dynamics which has not been fully understood.…”